Process for producing methyl phosphine oxides

ABSTRACT

METHYL PHOSPHINE OXIDES ARE PREPARED BY THERMAL ISOMERIZATION OF THE CORRESPONDING HYDROXYMETHYL PHOSPHINES. THE PRODUCTS FIND UTILITY AS FIRE RETARDANT ADDITIVES FOR ORGANIC POLYMERS SUCH AS POLYURETHANE FOAMS AND POLYESTERS, AND AS INTERMEDIATES FOR THE PRODUCTION OF SURFACTANTS, PLASTICIZERS, FIRE RETARDANT POLYMERS, AND GENERALLY OF OXIDATION STABILIZERS FORUSE IN LUBRICATIONG OILS, HYDRAULIC FLUIDS AND ORGANIC POLYMERS.

United States Patent Oflice 3,732,316 Patented May 8, 1973 3,732,316 PROCESS FOR PRODUCING METHYL PHOSPHINE OXIDES Kingso Chingtsung Lin, Newark, Ohio, assignor to Hooker Chemical Corporation, Niagara Falls, N.Y. No Drawing. Filed Nov. 12, 1970, Ser. No. 89,103 Int. Cl. C07f 9/50 US. Cl. 260-6065 P Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The thermal isomerization of certain phosphorus containing organic compounds is known. For example, tertiary phosphites have been thermally isomerized to produce the corresponding phosphonate derivatives. Likewise, phosphinite derivatives have been isomerized to produce phosphine oxides. In both instances, the isomerization reaction involved the displacement of a PO-C linkage to form the group.

BRIEF DESCRIPTION OF THE INVENTION In accordance with this invention there is provided a process for the production of bis(hydroxymethyl)methylphosphine oxide which comprises heating tris(hydroxymethyl)phosphine at a temperature and for a time suflicient to isomerize tris(hydroxymethyl)phosphine to form bis(hydroxymethyl)methylphosphine oxide.

The isomerization reaction of the instant invention is conducted at a temperature between about 120-250 de grees centigrade. Preferably, temperatures between about 1402l0 degrees centigrade are employed. At temperatures as low as 120 degrees centigrade, the time required for completion of the isomerization reaction is correspondingly greater and at a temperature above 250 degrees centigrade, decomposition of the product increases sutficiently to exclude those temperatures for all practical purposes.

DETAILED DESCRIPTION OF THE INVENTION Tris(hydroxymethyl)phosphine has been regarded as a hazardous material because of its lability, leading to explosions upon heating. It has been discovered that the explosive property of tris(hydroxymethyl)phosphine is in essence an exothermic oxidative isomerization reaction, which if properly controlled, produces bis(hydroxymethyl)methyl phosphine oxide in excellent yields.

Thus, although tris(hydroxymethyl)phosphine decomposes quite rapidly at elevated temperatures in the absence of the temperature moderating influence of a solvent, it has been found that in the presence of a solvent such as dimethylsulfoxide, acetic acid, N-methyl pyrrolidone, N,N-dimethyl formamide, and the like, the conversion to bis(hydroxymethyl)methyl phosphine oxide is smoothly conducted to aflord the product in quantitative yields.

The product of the thermal isomerization of tris(hydroxymethyl)phosphine, containing predominately bis- (hydroxymethyl)methylphosphine oxide exhibits excellent flame retardant properties. Furthermore, the product is an intermediate for the preparation of surfactants and fabric softeners of the type H H (R0 CHmP cm and (RtNCHzhP CH3 in which R is alkaryl or alkyl, in which the alkyl group contains from 8 to 18 carbon atoms, or

in which n is from 5 to 20, which derivatives may be prepared by known methods.

Although applicants do not wish to be bound by any specific theory, it is believed that the very rapid decomposition of tris(hydroxymethyl)phosphine observed in the preparation of tris(hydroxymethyl)phosphine from tris- (hydroxymethyl)phosphonium chloride represents an acid catalyzed exothermic oxidation leading to the formation of a carbonium ion intermediate, such as,

POHz li -CH2 EXAMPLE 1 Isomerization of tris(hydroxymethyl)phosphine in dimethyl sulfoxide To milliliters of dimethyl sulfoxide in a round bottom flask equipped with a reflux condenser, was added 29.5 grams of tris(hydroxymethyl)phosphine. The solution was heated to between -165 degrees centigrade to initiate the reaction. The dimethyl sulfoxide solvent was refluxed in the reflux condenser to dissipate the heat of the exothermic isomerization. After the reaction had gone to completion as noted by the cessation of refluxing dimethyl sulfoxide, the solvent was distilled gradually to yield 11.3 grams of a long needled crystalline material have a boiling point at -174 degrees centigrade at 0.1 millimeter mercury absolute and a melting point of 9498 degrees centigrade. This crystalline material was determined to be bis(hydroxymethyl)methyl phosphine oxide.

A low boiling dimethyl sulfide fraction of the distillate having a distinctive odor demonstrated that some of the oxygen from the dimethyl sulfoxide solvent had been extracted by the tris(hydroxymethyl)-phosphine. Nuclear magnetic resonance data obtained from the product demonstrated that 60% of the product was bis(hydroxymethyDmethyl phosphine oxide and 40% of the product was tris(hydroxymethyl)phosphine oxide.

EXAMPLE 2 oxide in 100% conversion. This result was established bythe titration of the tris(hydroxymethyl)phosphine content in the reaction product with iodine which demonstrated that only a trace amount of tris(hydroxymethyl)phosphine remained in the product. Phosphorus 31 nuclear magnetic resonance data for tris(hydroxymethyl)phosphine shows a +24.1 p.p.m. chemical shift employing 85% Phosphonc acid as a reference, whereas the thermally rearranged product gave an approximate -50 p.p.m. chemical shift using 85% phosphoric acid as the reference, indicating the presence of a phosphine oxide. The infrared spectrum of the rearranged product showed a strong absorption band at 1160 reciprocal centimeters indicating the presence of the P=O bond and at 1300 reciprocal centi- EXAMPLE 3 Assuming that the intermediate of the thermal rearrangement of 'tris(hydroxymethyl)phosphine to bis(hydroxymethyl)methyl phosphine oxide is the presence of an acid would favor the isomerization. Therefore t'r'is(hydroxymethyl)phosphine was refluxed in acetic acid for 7"hours. The acetic acid was distilled off under reduced pressure and it was determined that an amount of acetic acid had been consumed which was equivalent to the tris(hydroxymethyl)phosphine on a molar to molar basis. The'liquid product was distilled to give a product with alboilingpoint between 120-170 degrees centigrade at 0.5 millimeter of mercury absolute which constituted an 80% yield 'based upon the hypothetical structure Nuclear magnetic resonance spectroscopy demonstrated the presence of various phosphorus compounds in the product. The structures of the main product constituents weredetermined by infrared spectroscopy. The structures of these compounds appear as:

CH3i GHzO( JCHa boiling point 69100 C./ 0.35 mmqHg abs. 11 1.4740.

I ll CHsP CHzOCCI-ia 2 boiling point 100-120 C./0.35 mm.Hg abs. n 1.4748.

0 OHai .CHgO( JCHa CHzOH boiling point 120-165C./0.35 mm. Hg abs. 11 1.4700.

EXAMPLE 4 A solution of .tris(hydroxymethyl)phosphine (324 grams, 2.54 moles) containing 22% tris(hydroxymethyl) phosphine oxide, and 200 millilitersof N-methylpyrrolidone, was added dropwise to 240 milliliters of N-methyl pyrrolidone at about 170-175 degrees centigrade during a two hour period. The solution was heated for an additional 4 hours after completion of the introduction of tris(hydroxymethyDphosphine (subsequent experiments demonstrated thatheating for about 1 houris sufficient to insure complete reaction). The solvent was stripped off by heating on a steam bath under reduced pressure to yield 326 grams of va thick liquid product. Phosphorus nuclear.magneticresonance analysis of the liquid product indicated that it contained between 78-79% of his- (hydroxymethyl)methyl phosphine oxide and between 21- 22% of tris(hydroxymethyl)phosphine oxide, the two components demonstrating the chemical shift basedupon 85% phosphoric acid as the reference equal to -50.4 p.p.m. and -47.4 p.p.m., respectively.

Analysis.Calculated for C H PO (percent): C, 29.04; H, 7.31; P, 25.00. Found (percent): C, 30.16, H, 7.33; P, 23.59.

Esterification of 93.6 grams (0.74 mole) of the rearranged product with 173.7 grams of acetic anhydride, grams of acetic acid and 3.1 grams of anhydrous sodium acetate gave 94 grams (61%) of bis(acetoxymethyl)methy1 phosphine oxide (CH COOCH P(O)CH exhibiting a boiling point of -160 degrees centigrade at 0.3 millimeter mercury absolute and 28 grams (20%) of tris(acetoxymethyDphosphine oxide exhibiting a boiling point of -175 degrees centigrade at 0.3 millimeter mercury and having a melting point of 45-55 degrees centigrade. Redistillation of the acetate of bis(hydroxymethyl)methyl phosphine oxide yielded a product exhibiting a boiling point of 145-147 degreescentigradeat 0.3 millimeter mercuary absolute; the refractive index of 11 equals 1.46 58, phosphorus nuclear magnetic resonance demonstrated a chemical shift to 40.3 p.p.m. (referred to H PO and an acetate of 'tris(hydroxymethyl)phosphine oxide exhibiting a boiling point of -179 degrees Centigrade at 0.3 millimeter mercury absolute; having a melting point between 50-55 degrees centigrade.

Analysis.-Calculated for (CH COOCH P(O)CH (percent): C H O P, C, 40.39; H, 6.29; P, 14.88. Found (percent): C, 40.15; H, 6.41; P, 15.09.

Analysis.Calculated for (CH COOCH P(O) (per: cent): C9H15PO7, C, 40.64; H, 5.68; P, 11.95. Found (percent): C, 39.85; H, 5.89; P, 11.95.

EXAMPLE 5 Heating bis(hyroxymethyl)methyl phosphine oxide at temperatures higher than 230 C. resulted in a series of complicated reactions. For instance, the isomerized bis- (hydroxymethyl)methyl phosphine oxide containing product of Example 2 was subjected to distillation under reduced pressure of 0.1-0.3 millimeter mercury absolute at an ultimate temperature of 230 degrees centigrade to afford the following products.

(1) Distillate: (30% of the starting material) a mixture of various phosphorus compounds, boiling point 120- 160 degrees centigrade at 0.1-0.3 millimeter mercury absolute. These compounds appear to be the decomposition products of bis(hydroxymethyl)methyl phosphine oxide.

(2) Residue: (50% of the starting material) a dimerresinous material,

CHQOCH:

Molecular Weight: Ca1culated212. Iound209.

(3) Distillate trap: (20% of the starting material) water and formaldehyde.

The dimer of (2) is soluble in water and is intumescent upon the application of flame. The infra-red spectrum of the decomposed product of (1), which is carried out of the distillation flask withthe formaldehyde and water of (3), displayed several complicated P-H absorption bands. It was believed that the major product of this distillate was of the formula 0 CHKi -GHZOH EXAMPLE 6 The rearranged product of isomerization of tris(hydroxymethyl)phosphine (THP) containing 75% bis(hydroxymethyl)methyl phosphine oxide and 25% tris(hydroxymethyl)phosphine oxide when employed as an additive in the production of polyurethane foam afforded a polyurethane foamiproduct which did not burn upon direct contact with flame.

Bis(hydroxymethyl)methyl phosphine oxide when used as an additive for polyurethane foams and compared to diethyl N,N bis(2-hydroxyethyl)aminomethylphosphonate in accordance with ASTM Test 1692, afforded the following results. The same polyurethane foam material with diethyl N,N-bis(2-hydroxyethyDaminomethylphosphonate and bis(hydroxymethyl)methyl phosphine oxide was studied for hydrolytic stabilities at 70 degrees centigrade, at one weeks exposure and 100% relative humidity to afiford the results indicated in the following table:

3 The process of claim 1 wherein said polar solvent has a boiling point from about 120 to about 250 degrees centigrade.

Hydrolytio stablitg at k Pol re- 70 wee tl i ne, 100% relative o u ,parts parts ASTM Test 1692, fire retardant humldlty CH P(O)(CH2OH)z:

5 95 Self-extinguishing Go d- {J0 Non-burning D0- (C2H5O)zP(O)CH2N(CH2CH20H)2:

95 Not self-extinguish1ng D0. 90 Self-extinguishing Do. 80 Non-burning Do.

This comparative data demonstrates that the isomerization product of this invention is approximately twice as eifective as the known fire retardant additive for polyurethane foams, providing a non-burning product of good hydrolytic stability with 10 parts of additive.

What is claimed is:

1. A process for the production of a methyl phosphine oxide which comprisesheating a hydroxymethyl phosphine, in an inert polar solvent, at a temperature and for a time sufficient to isomerize the hydroxymethyl phosphine to form a methyl phosphine oxide.

2. The process of claim 1 in which said hydroxymethyl phosphine is heated to a temperature from about 120 to about 250 degrees centigrade to form said methyl phosphine oxide.

References Cited UNITED STATES PATENTS WERTEN F. W. BELLAMY, Primary Examiner U.S. Cl. X.R.

2602.5 A], 2.5 AM; 2S2-49.8 

